1. Field of the Invention
This invention relates to an apparatus for magnetically recording and/or reproducing an information signal comprised of at least an audio signal and an index signal for use in controlling transportation of the tape.
2. Description of the Prior Art
As is shown on FIG. 1, in accordance with a standard track format for an 8 mm video tape recorder, successive tracks, only one of which is indicated at 2, are formed obliquely on a magnetic tape 1 and are scanned alternately by two rotary magnetic heads which are angularly separated by 180.degree.. The length of each track 2 corresponds to rotation of the respective head through an angle of 221.degree.. A part 2S of each track 2 extending from its starting point and corresponding to rotation of the rotary head through an angle of 36.degree., is used for recording an audio signal. The remaining part 2V of the track corresponds to head rotation through an angle of 185.degree. and is used for recording a video signal.
Each audio track part 2S is divided into successive areas 21-25. The area 21 is designated a scanning starting area for the rotary head, the area 22 is a preamble area in which a clock run-in is recorded, the area 23 is an audio data area for recording a PCM audio signal, the area 24 is a postamble area for providing a back margin in case of an after-recording operation, and the area 25 is a guard area between the track parts 2S and 2V.
The PCM audio data recorded in the area 23 corresponds to a stereo audio signal of one field period that is time-base compressed and PCM coded and includes an error correcting code, an ID code and the like. The data format for writing the PCM data, error correcting code (CRCC), ID code and the like into a memory with interleaving and time-base compressing is disclosed in U.S. Pat. No. 4,562,578, issued Dec. 31, 1985 and having a common assignee herewith. It has been disclosed to convert the signal recorded in each of the areas 22, 23 and 24 into a by-phase mark signal of 2.9 MHz when the value is "0" and of 5.8 MHz when the value is "1", before being recorded in each of such areas, for example, as in U.S. Pat. No. 4,551,771, issued Nov. 5, 1985 and also having a common assignee herewith.
The video track part 2V is shown to be divided into an area 28 following the guard area 25 and corresponding to rotation of the respective head through an angle of 180.degree. and an area 29 corresponding to rotation of the head through the remaining angle of 5.degree.. A frequency-multiplexed signal composed of an FM signal modulated by a luminance signal, a low-frequency converted carrier chrominance signal, an FM signal modulated by a monaural audio signal and a pilot signal for one field is recorded in and/or reproduced from the area 28. The area 29 is a scanning terminating area for the rotary head.
The above-described format allows the ID code to be recorded in the audio data area 23 together with the audio signal. Therefore, a variety of data, such as, the recording date, the absolute position along the tape, the program number, the scene cut number, the recording tape speed, whether the audio signal is stereo or monaural, or bi-lingual, and whether dubbing is possible, can be recorded and then utilized, for example, in a search mode for locating a desired starting point during reproduction, editing and the like.
However, by reason of the interleaving, the ID codes are recorded with the PCM audio data in a scattered manner. It is therefore necessary that the rotary head correctly scan the area 23 over a substantial length thereof in order to correctly reproduce the ID codes. However, in the search mode, the tape 1 is transported at a high speed, for example, 30 times higher than that used in the recording mode, so that the rotary head scans the area 23 obliquely, whereby the rotary head cannot correctly reproduce the ID codes scattered over the length of area 23.
To cope with the above problem, it has been proposed to record index signals, such as, the ID codes and so on, in the postamble area 24 of the audio track part 2S. For example, in U.S. Pat. Application Ser. No. 06/885,203 (filed July 14, 1986) and also having a common assignee herewith, and in the corresponding European laid-open Patent Application No. 0209151, it is disclosed to encode various data to be recorded in such postamble area 24.
The area 24 has a length corresponding to rotation of the rotary head through an angle of 2.06.degree.. Since one field of video is recorded in area 28 of video track part 2V which corresponds to rotation of the head through 180.degree., and since there are 262.5H (H=one horizontal period) in each field, the area 24 corresponds approximately to a time period of 3.0H.
The postamble 24 is, for example, divided into a first area 241 of 1.5H and a second area 242, also of 1.5H, as shown in FIGS. 2A and 2B. In the area 241 there is recorded a postamble signal exclusively formed of "1"s for the PCM audio signal recorded in the area 23. In the initial 0.5H period of the area 242, there is recorded a preamble signal exclusively formed of "1"s, and a coding index signal CDIX, which has the same contents as the encoded ID code, is recorded in the remaining 1H period of the area 242. The preamble signal recorded in the initial 0.5H period of the area 242 and formed exclusively of data "1"s of 5.8 MHz, is used, for example, as a clock run signal for the subsequent coding index signal CDIX.
The coding index signal CDIX is equally divided into six blocks BLK1-BLK6 and a preparative area or auxiliary block BAUX, as shown in FIG. 2D. Further, each of the blocks BLK1-BLK6 is comprised of 51 bits divided into a 3-bit mark code MK used as a header for the data read, five 8-bit ID codes ID0-ID4 and an 8-bit CRC code CRCC provided for the ID codes ID0-ID4, as shown in FIG. 2E.
The blocks BLK1-BLK6 correspond to Modes 1-6, respectively, to which the ID codes IDO-ID4 recorded in the PCM audio data area 23 belong. The ID codes ID0-ID4 in the blocks BLK1-BLK6 are the same as the ID codes ID0-ID4 recorded in the area 23 which may be signals indicative of an absolute position on the tape 1, cut numbers designated each scene of the recorded contents, the recording data and time, and so on.
The ID codes ID0-ID5 interleaved with the PCM data and recorded in the PCM audio data area 23, as disclosed in U.S. Pat. No. 4,562,578, are recorded in a range of one field or one track corresponding to rotation of the head through an angular extent of 36.degree. in the PCM audio data area 23. It is therefore necessary to provide at least six tracks for recording all of the information of the six blocks, that is, all the bits forming the ID codes ID0-ID5. Accordingly, each unit of information, for example, the tape address, program number, and time code, is designated as one of the Modes 1-6 and recorded in correspondence to respective blocks BLK1-BLK6. For example, if the system selects a read-out of Mode 1, ID0=Mode Number 1, ID1=Hour, ID2=Minute, ID3=Second and ID4=Frame Number are displayed by the use of five ID codes ID0-ID4. If Mode 2 is selected, ID0=Mode Number 2, ID1=Program Number, ID2=Cut Number, ID3=Minute and ID4=Second are displayed.
The index signal CDIX in the area 242 is converted into a by-phase mark signal of 2.9 MHz when its value is "0" and of 5.8 MHz when its value is "1", and then recorded in the area 242 in the same manner as the signal recorded in the audio track 2S.
With the above-described recording format of the index signal CDIX, although the rotary head scans the track 2 obliquely with respect to the longitudinal direction of the track when the tape speed during reproducing is different from that for recording, since the area 242 is short, for example, has a length corresponding to 1.5H, the rotary head can scan the entire length of the area 242, or with correct tracking, even in the search reproducing operation, in which the tape transporting speed, is 30 times the tape speed for recording. Hence, it is certain the the index signal CDIX (ID codes) can be correctly reproduced.
The ID codes have different meanings dependent on the Modes 1-6. Therefore, if the ID codes recorded in the area 23 with the PCM audio data are used, it is necessary to reproduce six tracks, that is, six field periods have to be reproduced for obtaining the necessary ID codes. On the other hand, by the use of the format described above, since the ID codes for all the Modes 1-6 are recorded in the single area 242 as the index signal CDIX, it is sufficient to reproduce only one horizontal period within the area 242 and, hence, it is possible to immediately obtain the necessary ID codes.
The index signal CDIX can be recorded in a so-called after-recording operation after a video signal Sc and audio signals L and R have been recorded. For example, the ID code can be added to the already edited tape for identifying chapter numbers, as disclosed in Japanese Patent Applications No. 60-64554 and 60-161438.
However, if the index signal CDIX is recorded in the postamble area 24 as described above, problems can occur when the PCM audio signal is after-recorded or when the index signal CDIX is rewritten in the area 242.
These problems will be explained more specifically with reference to FIGS. 3A to 3E. FIG. 3A illustrates the audio track part 2S and the starting region of the video track part 2V shown in FIGS. 1 and 2A. The format shown in FIG. 3A may be considered a reference recording format. When the PCM signal is actually after-recorded by a video tape recorder (VTR), the areas 22, 23 and 24 may be deviated, as a whole, toward the track area 28, as shown in FIG. 3B, or, on the contrary, toward the starting point of the track 2, as shown in FIG. 3C, due to errors in the mechanism and/or the signal timing, jitter caused by tape friction and the like. Even in the case where the PCM audio signal is recorded simultaneously with the video signal, the areas 22, 23 and 24 may be deviated from their reference positions, as shown in FIGS. 3B and 3C, due to the causes specified in the case of after-recording.
Thus, if a PCM signal is after-recorded on a track 2 which has its areas 22, 23 and 24 deviated from the reference positions as shown in FIG. 3B, and such after-recording is effected by a VTR which records the areas 22, 23 and 24 with the deviations shown in FIG. 3C, the resulting recorded track 2' is as shown in FIG. 3D. More specifically, the areas 22', 23' and 24' on FIG. 3D are newly formed by the after-recording. In this case, however, the old area 24, and especially the area 242 thereof, still remains between the new area 24' and the video track area 28. When the rotary head scans the track 2' thus formed, the new index signal CDIX is reproduced from the new area 242' and the old index signal CDIX is reproduced from the old area 242. Accordingly, when the index signal CDIX is used for a variety of control operations the fact that index signals are reproduced from the old and new areas 242 and 242' inevitably causes problems.
Moreover, if only the index signal CDIX is recorded in the area 242 on the track 2 recorded as shown in FIG. 2C by the use of a VTR which records signals with the deviations shown in FIG. 3B, the new areas 241' and 242' are formed following the old areas 241 and 242, as shown in FIG. 3E, provided that the tolerable range of the deviations of the areas 22, 23 and 24 is regulated to be between +1.5 and -1.5 horizontal periods. In such case, the end portion of the old area 242 is more or less erased by the starting end portion of the new area 241'. Since the new area 242' and the old area 242 both exist in this case, problems again are inevitable in the reproducing operation.